Tensile support structures, such as coated steel belts or wire ropes containing metal cords, are used to move an elevator car up and down within an elevator shaft or hoistway. Because the condition of the tensile support structure is critical to the safety of the operation of the elevator, there is a need to determine the remaining strength level of the tensile support and detect if the remaining strength level falls below a minimum threshold.
The strength of a tensile support structure can be reduced by normal operation of the elevator over time. The primary source of the degradation in the strength of the support structure is the cyclic bending of the support structure around sheaves as the elevator is moved up and down in an elevator shaft or hoistway. The degradation of a support structure is normally not uniform along the length of the support structure, but rather, focused to areas of the support structure that are subjected to high levels or severities of bending cycles.
Some electrical characteristics, such as electrical resistance or impedance, of the cables, cords or tension members in the support structure will vary as the cross-sectional areas of the tension members decrease. Accordingly, it is possible to determine the remaining support strength of the support structure based on the electrical characteristics of the tension members thereof. There currently are some monitoring systems which employ a resistance-based inspection scheme to monitor the resistance of support structures, and thus, the remaining strength thereof. Such systems are built upon microprocessor based designs, which utilize several analog to digital and/or digital to analog interfaces, and other added implementations for processing digital signals. The digital nature of such systems further rely on sampled data, and thus, are unable to provide continuous monitoring or immediate responses to detected fault conditions.
Accordingly, there is a need for a system and method for monitoring that is less complex and more cost-effective. Alternatively or in addition, there is a need for systems and methods that are capable of providing continuous monitoring of support structures and immediate response to detected fault conditions. Finally, there is an alternative or additional need for a monitoring system that allows for easier and more accurate calibrations thereof.